1. Field of the Invention
The present invention relates to water-in-oil vaccine formulations, processes of making the formulations and the use of such formulations for the vaccination of animals.
2. Background Art
The cornerstone of many infectious disease control programs is induction of specific immunity by vaccination with either live or inactivated microorganisms or their products. An effective vaccination procedure allows the development of a state of immunologic memory in an animal for an antigen, which leads to a rapid and robust immunological response in the animal, upon subsequent contact with the antigen. Some antigens, however, are only weakly immunogenic. Such antigens may be unable to induce an immune response sufficient to provide an effective protection for the animal upon subsequent challenge, or may require administration with additional agents that boost immunogenicity to provide effective protection.
The immunogenicity of an antigen can be increased by administering it in a mixture with substances, called adjuvants, which increase the response against the antigen either by directly acting on the immune system or by modifying the pharmacokinetic characteristics of the antigen and thereby increasing the interaction time between the latter with the immune system.
Emulsions made from water and oil (e.g., water-in-oil, oil-in-water, water-in-oil-in-water emulsions) can be used as adjuvants in vaccines. Water-in-oil emulsions are commonly used as adjuvants in animal vaccines, e.g., in poultry vaccines. In general, to make a water-in-oil emulsion, an aqueous phase antigen is slowly added to a mineral oil carrier in the presence of one or more emulsifying agent(s), resulting in micelles consisting of oil droplets within which the aqueous antigen resides. It is believed that the oil component induces the migration of immune cells to the injection site, and also serves to protect the antigen and extend the period of time for the immune cells to process the antigen. The end result is an enhancement of the immune response as compared to simply injecting the antigen by itself.
Adjuvants consisting of acrylic polymers are sometimes used as alternatives to oil-based emulsions in vaccine formulations. An exemplary acrylic polymer is a water-soluble polymer of acrylic acid crosslinked with polyallyl sucrose which is also known as Carbopol®. U.S. Pat. No. 5,026,546, for example, refers to the use of dimethyl dioctadecyl ammonium bromide (DDA) as a vaccine adjuvant and the addition of Carbopol® to improve the solubility of DDA in water.
Both oil-based emulsions and acrylic polymers have distinct advantages when used as adjuvants in vaccine formulations. Combining water-in-oil emulsions and acrylic polymers, however, would have been discouraged since it is expected that acrylic polymers such as Carbopol® would be highly reactive in association with an oil emulsion. For example, U.S. Pat. No. 5,026,546, discussed above, mentions the use of Carbopol® but provides no suggestion of using DDA and/or Carbopol® in water-in-oil or oil-in-water emulsions. In addition, with regard to adjuvants for certain species such as poultry, acrylic polymers have been avoided due to their perceived high reactivity in general. Thus, there exists a need in the art for novel adjuvants which provide the combined advantages' of acrylic polymers and water-in-oil emulsions without the drawbacks of adverse reactivity caused by the acrylic polymers in the vaccinated animal.